Those who live in the Columbia Waterfront neighborhood of Brooklyn know that the big expanse of highway cutting off their neighborhood from the delights of Cobble Hill and Carroll Gardens is called “the trench.”

The trench — which also goes by the names Brooklyn-Queens Expressway and I-278 — was, since it was first conceived in the 1930s, a questionable asset. For many residents, it became another barrier in the 10-to-15-minute schlep to the F train. It came with soot, noise and the smell of carburetors. Plenty of people looking for homes in Brooklyn had zero interest looking west of Henry Street — either on the Carroll Gardens side of the highway or at the Columbia Waterfront.

“The highway creates a psychological boundary that if there was no highway, no one would think twice about,” says Jill Bernstein, who spent seven years living on Henry Street before she and her family ventured over the trench to the 25 Carroll St. condo development, just off Van Brunt Street and about 400 yards from the water.

And boy, is she glad. For those who have been willing to cross that border, life is decidedly not trench warfare. It’s on the upswing.

Almost all the waterside buildings that came on the market in the depths of the recession have sold out — or are well on their way — and developers, restaurant owners and old and new Brooklynites are feeling good about snuggling up next to the BQE.

“What we love about living over here is that it’s relatively close to Court Street and Smith Street, but you have this little community, cut off by [the highway] that’s its own little neighborhood,” says Robin Marshall, who, with her husband, Russ Moorehead, bought her first apartment in the Columbia Waterfront nabe in 2005 and last year upgraded to a 1,350-square-foot, three-bedroom condo at Columbia Commons with their son, Marshall. The building is across the street from the trench.

“Everyone needs a half-mile walk every day,” she jokes. “It’s good for you!”

“When we first looked, six or seven years ago, [anything beyond Henry Street] seemed too remote,” says Bernstein, who, with her husband, Michael Phillips, bought a 25 Carroll St. duplex that they closed on in August and now live in with their son and daughter. “But we watched the neighborhood turn over.”

For one thing, Bernstein’s gym was there. “Some of the restaurants we go out to were there. [Mother] Cabrini Park was over there,” she says. “We just started to like it over there.”

Even one of the great markers of gentrification appeared when the James Beard Award-winning Portland chef Andy Ricker announced that he’s opening a Pok Pok on Columbia Street, the neighborhood’s main artery. He says the Thai restaurant should open in the next couple of months.

“I spent a bunch of time researching neighborhoods,” says Ricker, “and Red Hook came up on top, but I couldn’t find the space. As I kept going through Columbia Waterfront on my way out there, I kept thinking, ‘Wow, this is such an interesting neighborhood.’ ”

“We were pleasantly surprised how much people embraced the location,” says Lindsay Barton Barrett, of the Corcoran Group, who sold 25 Carroll St. “All the units were really, really quickly closed.”

In fact, Bernstein and Marshall’s buildings are both sold out. The 17-unit 25 Carroll St. sold at a respectable average of $670 per square foot — and the 42-unit Columbia Commons fetched an impressive $750 per square foot, according to Streeteasy. And the success of these buildings (and others nearby) are drawing other developers to the area.

Andrew Booth at the Corcoran Group will be putting nine apartments on the market at 49-53 Summit St., between Columbia and Van Brunt streets, in the next two to three weeks. The condos will range from 900-square-foot one-bedrooms, starting at $550,000, to up to 2,400-square-foot three-bedrooms priced at $1.4 million. And Veronika Fernandez, development coordinator for AVO Construction, which is building 49-53 Summit, says her firm also just acquired a lot on Kane Street off Columbia. They’re planning a ground-up condo building that should hit the market in 2013.

A little farther south, Booth has already started selling 49 Woodhull St., a 10-unit condo building that will be ready this spring, with prices ranging from $569,000 for a 1,000-square-foot two-bedroom to $950,000 for a 1,333-square-foot three-bedroom. So far, seven out of 10 units have sold.

On the same block, Booth’s colleague, Nicole Galluccio, just sold the last of three units at 35 Woodhull St., a townhouse that is being converted to condos. Galluccio is also working on another smaller-scale conversion at 118 President St., between Hicks and Columbia, a four-unit building consisting of two- and three-bedrooms.

And last November, one of the staples of the neighborhood, Sokol Bros. Furniture on Columbia Street, which had been around for 62 years, was sold. Speculation that apartments would rise in its place began almost immediately.

The only question seems to be, how close to the highway can you get?

At 100 Luquer St. on the Carroll Gardens side of the trench, the highway is within spitting distance. “Initially the developer had it on the market as condos,” says David Behin of MNS about the brand-new rental, which anticipates getting its certificate of occupancy in about a month. After inking contracts on several units, however, the developer switched to rentals, and the anticipated rents are bold. “Probably about $4,000 to $5,000 [per unit], depending on floor,” says Behin of the two-per floor, 1,080-square-foot apartments (plus one ground-floor, 1,800-square-foot duplex).

Just next door, at 671 Henry St., another five-unit building is gearing up to go on the market as rentals.

“I’d say we’re 90 percent completed,” says Paul Valentino, owner of the property. (These apartments will be significantly less expensive — Valentino estimates asking between $2,500 and $3,500 per unit, although he is not certain yet.)

Of course, the biggest residential project on either side of the BQE has been One Brooklyn Bridge Park, the massive 437-unit condo development (where about 300 units have sold for an average of $834 per square foot), which lies just outside the Columbia Waterfront neighborhood boundaries. It offers the one big thing that widened the eyes of people who live by the trench: amenities.

Currently, One Brooklyn Bridge’s commercial space is occupied by Waterfront Wine and Spirits, plus a doggie spa called the Wag Club. And then there is the park itself, that came with the building. (And there is a big push to put in a 2-acre, $12 million riverside park, from Degraw to Kane on Columbia Street.)

But the area around the BQE could still use more.

“What I would love is a little market,” says Marshall. “Other than the delis, there isn’t anything. I wish Union Market would open up an outpost.”

Marshall might be in luck. “We’re working on [getting] a wine bar” in some of the commercial space, says Penelope Stipanovich, director of sales at One Brooklyn Bridge Park. “We are heavily targeting supermarkets and grocery stores. There’s been major interest from some of the major chains.”